1. Field of the Invention
The present invention relates to an inspection apparatus used for a device substrate of a semiconductor device and to an inspection method using the inspection apparatus. More particularly, the present invention relates to an inspection apparatus of non-contact type and an inspection method using the inspection apparatus.
2. Description of the Related Art
In recent years, attentions have been given to a technique of forming a thin-film transistor (TFT) using a semiconductor film (whose thickness is about several nm to several hundred nm) formed on a substrate having an insulating surface. This is because there is increasing demand for an active matrix semiconductor display device that is one type of semiconductor devices. Typical examples of the active matrix semiconductor display device include a liquid crystal display, an OLED (organic light emitting device) display, and a DMD (digital micromirror device).
It is possible to obtain a high mobility with a TFT (crystalline TFT) that uses a semiconductor film having a crystal structure as an active layer. Therefore, it is possible to realize an active matrix semiconductor display device that performs high-definition image display by integrating functional circuits on the same substrate.
By the way, the active matrix semiconductor display device is obtained through various manufacturing steps. In the case of an active matrix liquid crystal display, for instance, there are mainly included a pattern forming step for forming a semiconductor film and performing pattern formation, a color filter forming step for realizing colorization, a cell assembling step for forming a liquid crystal panel by sealing a liquid crystal between a device substrate having an element including a semiconductor and an opposing substrate having an opposing electrode, and a module assembling step for finishing the liquid crystal panel as a liquid crystal display by attaching driving parts for driving the liquid crystal panel and a backlight to the liquid crystal panel assembled in the cell assembling step.
The manufacturing steps described above also include an inspection step, although this inspection step differs to some extent depending on which type of the liquid crystal display will be produced. If it is possible to find defective items at an early stage in the manufacturing steps before the liquid crystal display is finished as a product, it becomes possible to omit the following manufacturing steps for each of the defective panels. Accordingly, the inspection step is an extremely effective means from the viewpoint of cost reduction.
One type of the inspection step included in the pattern forming step is a defect inspection that is performed after the pattern formation.
The defect inspection after the pattern formation means an inspection for detecting each spot, in which a malfunction occurs due to variations in the width of a semiconductor film pattern, insulating film pattern, or wire pattern (hereinafter simply referred to as the “pattern”), after the pattern formation. Alternatively, the defect inspection means an inspection for detecting each spot in which wire breaking or a short circuit occurs due to dust or a film formation failure. Also, in some cases, the defect inspection means an inspection for confirming whether a circuit or a circuit element that is an inspection target operates normally.
Such defect inspections are broadly divided into an optical inspection method and a probe inspection method.
The optical inspection method refers to an inspection method with which a pattern formed on a substrate is read using a CCD or the like and each defect is identified by comparing the read pattern with a reference pattern. Also, the probe inspection method means an inspection method with which minute pins (probes) are set up on terminals on the substrate side and each defect is identified with reference to the magnitude of a current or a voltage flowing between the probes. In general, the former method is called the “non-contact type inspection method”, while the latter method is called the “sensing pin type inspection method”.
It is possible to detect each defect of a device substrate regardless of which method described above is used. However, each of the inspection methods described above has a shortcoming.
In the case of the optical inspection method, if an inspection is performed after the formation of several pattern layers is finished, it becomes difficult to identify patterns formed as lower layers and therefore it is difficult to detect each defective spot. However, if an inspection is performed each time a pattern is formed, the inspection step itself becomes complicated and the time taken by the whole manufacturing steps is elongated. Also, in the case of the probe inspection method, probes are directly set up on wires, so that there may be cases where the wires are damaged and minute dust is caused. The dust caused in the inspection step becomes a factor for the reduction of yield in the following steps and therefore is not preferable.